Embolic stroke is among the leading mortality factors for adults, and is a major cause of disability. A common cause of embolic stroke is the release of thrombus that may form in the left atrial appendage (“LAA”) as a result of atrial fibrillation. The LAA is a small windsock-like cavity that extends from the lateral wall of the left atrium of the heart, generally at the level between the mitral valve and the root of the left pulmonary vein. The LAA normally contracts with the left atrium during systole so that blood in the LAA is ejected into the left atrium and then into the left ventricle. During atrial fibrillation, however, the LAA fails to vigorously contract due to the lack of synchronicity of the electrical signals in the left atrium. As a result, blood may stagnate within the LAA and thrombus may form in the stagnant blood that pools within the LAA. That thrombus eventually may subsequently be ejected into systemic circulation after a normal sinus rhythm is reinstituted, potentially traveling to the brain and resulting in a stroke.
When treated surgically, the entry to the LAA is obstructed to prevent blood flow between the atrium and the LAA. This may be accomplished in a number of ways, for example, by filling the atrial appendage with a biocompatible material, or by securing a plug in the ostium of the LAA, or by suturing or stapling the opposing walls of the appendage together, after which the LAA may be resected and removed.
Challenges exist for isolating or removing the LAA. For example, the LAA tissue may vary in thickness, with some parts being extremely thin or friable and susceptible to tearing. Consequently, traditional methods of suturing or stapling may present a high risk of bleeding at the puncture site. Moreover, LAA procedures typically are performed as an adjunct to more comprehensive surgical procedures, when the patient is on a heart-bypass machine, and bleeding associated with the typical open or thorascopic methods of occlusion of the LAA generally does not become apparent until the patient is taken off the machine and the heart begins pumping again. If bleeding does occur through the suture or staple puncture points, the patient may need to be put back on the bypass machine to stop the bleeding which exposes the patient to significant additional risk and morbidity.
Known methods for preventing such problems with the LAA have drawbacks. In particular, most of the previously-known devices are designed for a theoretically ideal LAA anatomical structure having a well-defined, symmetrical, and typically circular ostium and expected depth and orientation of the LAA cavity. Such ideal anatomical geometry is rarely, if ever, encountered. Among the devices currently in use is a hairpin-shaped clip (Ligaclip) that may be placed exteriorly over the juncture of the LAA and atrium so that the legs of the clip can be deformably squeezed together along the juncture. Such clips have been reported, in some instances, to fail to fully occlude the hollow structure to which they were applied. Other devices that employ a loop applied to the base of the LAA on the pericardial surface may abrade the pericardial surface, potentially leading to fatal cardiac pericarditis or pericardial tamponade. Other devices involve using expandable disks to clamp and collapse the LAA tissue, but these, too, rely on the LAA having reasonably symmetric and well-defined depth and anatomy and have issues around sealing at tissue puncture points. There remains a need for devices and techniques for occluding hollow anatomical structures such as, for example, the LAA, that avoid the foregoing difficulties.